Relationship between relative water content, nitrogen pools, and growth of Phaseolus vulgaris L. and P-acutifolius A.!Gray during water deficit

Phaseolus acutifolius A. Gray is a potential source of stress-tolerant traits for Phaseolus vulgaris L. through interspecific hybrids. The objective of this study was to quantify the effects of water-deficit stress on vegetative growth, shoot relative water content (RWC), and leaf concentrations of proline, polyamines, and related metabolites in P, vulgaris compared with P, acutifolius, Stress-induced changes in N metabolism putatively related to stress tolerance have not been investigated previously in P. acutifolius. Replicate pots, each containing three 5-d-old plants in 18.9 L of soil with 4 L of available water, were subjected to water deficit by withholding water (terminal drought) or were maintained under well-watered (control) conditions. Compared with controls, stressed plants of both species accumulated approximately 55% less shoot dry matter. Root dry matter accumulation was inhibited to a greater degree in P. acutifolius (approximate to 70% for two genotypes) than in P, vulgaris (14 and 27% for two genotypes), P, acutifolius maintained greater shoot RWC than P, vulgaris, In droughted plants of P, acutifolius, Leaf arginine and proline concentrations did not change, total polyamine (Sigma agmatine + putrescine + spermidine + spermine) concentrations decreased, and ammonia increased compared with controls. In P, vulgaris, water deficit increased concentrations of arginine (>30%) and proline (>300%), whereas total polyamine and ammonia concentrations did not change compared with controls, In all four genotypes examined, proline concentration was inversely related to RWC (R-2 greater than or equal to 0.90). Leaf proline concentration is an indicator of plant water status in Phaseolus but not of tolerance or sensitivity of vegetative growth to water deficit.